In the specification of U.S. Pat. No. 4,279,655, magnesia partially stabilised zirconia ceramic materials, which possess good thermal shock resistance and high strength and wear resistance, are described. As noted in that specification good thermal shock resistance and high physical strength had, for many years, been regarded as mutually exclusive properties of ceramic materials. However, by producing materials with a specified microstructure, this hitherto unforseen combination of physical properties was found to be achievable.
In some situations where ceramic materials may be used, it is not necessary for the ceramic material to possess both exceptional strength and good thermal shock resistance. For example, for low temperature applications, such as in wire drawing and in bioceramics (synthetic joints for humans and animals), the strength and wear resistance of the ceramic is more important than its thermal shock resistance, but for high temperature applications, such as extrusion dies for brass, copper and steel, thermal shock resistance and reasonable strength are the essential attributes of the materials.
Most uses of ceramic materials can be categorised by reference to the temperature range in which the material is to function. To illustrate this point, examples of applications of ceramic materials are provided in Table 1 below (which is not intended as an exhaustive listing of the applications of ceramic materials).
TABLE 1 ______________________________________ TEMPERATURE OF USE APPLICATIONS ______________________________________ Low temperature Bio-prosthesis devices; dry (Room temperature bearings; wear resistant lining to about 400.degree. C.) and tiles; guides for wire bars and threads; sizing tools for the powder metallurgy industry; scraper blades for the coal industry and other mining indus- tries; tappet (cam follower) facings; valve guides, valves and seals; nozzles for auto- claves, (for example in paper making); nozzles for slingers and hydro-cyclones; dies for wire drawing, cold tube drawing, powder compaction and injec- tion moulding of plastics; pump (including slurry pump) liners, spindles, seals and pistons; abrasive and corrosive chemical handling apparatus. Intermediate tempera- Engine components such as valve tures (from about 400.degree. C. guides and cylinder liners; to about 700.degree. C.) powder extrusion dies; dies for hot extrusion of aluminium metal; some induction heating equipment components; non- ferrous liquid metal pump parts. High temperatures Brass, copper and steel extru- (from about 700.degree. C. sion dies; engine components to about 1000.degree. C.) such as hot plates, piston tops and valve seats; non-ferrous liquid metal pump parts. Very high temperatures Dies for extrusion of steel, (in excess of 1000.degree. C.) zirconium, titanium and other difficult metals. ______________________________________
It is an objective of the present invention to provide ceramic materials which have properties that make them particularly suitable for use in a required temperature range.